The ultimate goal of clinicians treating patients with movement dysfunction is to restore normal movement This restoration of normal movement can only be accomplished with knowledge of the normal patterns of movement. These normal patterns of movement are produced by an interaction of neural circuits, primarily in the spinal cord, and the musculoskeletal system. Patterns of output element (traditionally defined muscles and/neuromuscular compartments) activity (synergies) underlie the movement trajectories used during volitional movement and during movement evoked by perturbations, such as those induced by stretch. The aims of this project are to: l) determine the synergies underlying specific volitional and perturbation-evoked movements that have the same trajectory, and determine whether these synergies are the same; 2) determine if altering perturbation-evoked synergies using newly developed operant conditioning methods alters the matching volitional synergy; 3) repeat studies for aims l & 2 in patient subjects to determine whether we can develop a treatment tool to affect movement in patients with movement dysfunction. The results of this study will provide information on normal movement, but more importantly provide a logical rationale for treating patients with movement dysfunction.